Cardiac pacemakers and other implantable stimulation devices such as cardioverters and defibrillators, are hermetically sealed within a housing or casing (sometimes also referred to as a “can”) to isolate the electronic circuits contained within the device from the body environment. Such devices require that electrical signals be reliably passed between the hermetically sealed circuitry and external connectors without compromising the hermeticity of the device. Depending on the configuration of the implantable device there may be multiple electrical paths required between the device and its external connectors for delivering, for example, multi-chamber or multi-site stimulation and shock therapy, and for receiving sensed cardiac signals. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term connection means, typically in the form of a component usually referred to as a header, that does not compromise the hermetic package. The header typically incorporates a plurality of receptacles for receiving the electrical connector assemblies of corresponding leads such as one or more bipolar pacing/sensing leads and/or one or more cardioverting/defibrillating leads. The receptacles contain terminal contacts electrically connected to the hermetically sealed electronic circuitry via a feedthrough assembly.
When a patient's heart does not function normally due to a genetic or acquired condition, various treatments may be prescribed to correct or compensate for the condition. Pharmaceutical therapy may be prescribed for the patient or an ICD may be implanted in the patient to administer cardiac resynchronization therapy (CRT). CRT delivers electrical impulses to the heart's two lower chambers (the ventricles) and one upper chamber (the right atrium) to improve the efficiency of each contraction of the heart and the amount of blood pumped to the body.
In conjunction with such therapy it may be desirable to continuously measure pressure in one or more chambers of the heart. For example, absolute cardiac pressure may be used as an indicator for several potentially lethal cardiac conditions. By measuring cardiac pressure, abnormal conditions may be detected and in some cases the patient's therapy may be modified to compensate for the abnormal conditions. As an example, if cardiac pressure is continuously measured, the operation of an implanted medical device such as an ICD may be adjusted as necessary according to conditions diagnosed as a result of the pressure measurements.
Conventionally, pressure sensing devices have been used to measure pressures on the right side of the heart. However, measurements of right side pressure may not provide sufficient indications for detection of conditions such as congestive heart failure, hypertension or mitral valve defects. In particular, left atrial pressure (LAP) has been identified as an excellent predictor of heart failure onset and progression. By accurately measuring LAP it becomes possible to administer preventive care before the onset of congestive heart failure thus preventing hospitalization.
Left atrial blood pressure may be measured directly in real time using a pressure sensor device incorporated into a distal end of a permanent or temporary endocardial lead. The lead is typically inserted into the right side of the heart and routed through an opening formed in a septal wall to gain access to the left side of the heart. The lead includes one or more sensors for measuring cardiac pressure on the left side of the heart and, if needed, the right side of the heart. The lead also includes an attachment structure that secures the distal end of the lead to the septal wall. The proximal end of the pressure sensing lead carries an electrical connector assembly configured to be received by a receptacle in the header of the implantable medical device which contains appropriate pressure measurement processing circuitry. For detailed descriptions of LAP measurement technology, see U.S. Pat. Nos. 6,328,699 and 6,970,742 both of which are incorporated herein in their entireties by reference.
Noninvasive telemetry has been developed allowing information such as data and control signals to be bidirectionally communicated, for example, by means of an electromagnetic energy link, between an ICD and an external system. Such an external system, typically comprising by way of example a controller, a programmer, a handheld interrogator, and/or a monitor, provides a convenient means through which the operation of the ICD may be controlled and monitored, and through which information sensed by the ICD can be read, interpreted, or otherwise used. In an electromagnetically-coupled system information is transferred from a transmitting antenna such as a telemetry coil within the ICD to a receiving antenna by way of a radiated carrier signal. The carrier signal is modulated with the data to be transmitted using an appropriate modulation scheme. The modulated carrier induces a voltage in the receiving antenna that tracks the modulated carrier signal. The received signal is then demodulated to recover the transmitted data.
The placement of a telemetry coil within a molded polymer header is known. By placing the coil outside of the hermetically sealed metal casing and within an enclosure fashioned of an electrically insulative material instead of inside the casing, the low pass filtering imparted by the casing is eliminated. Signals may thus be transmitted and received at high carrier frequencies providing high bandwitdh communication. It would be desirable to incorporate a telemetry coil within the confines of the standard, typically multiport headers of existing ICDs in an efficient, compact manner with minimal modification of the existing unit and without alteration of the external configuration of the existing header. It would also be desirable to dedicate such telemetry coil to the transmission of sensed LAP data to an external system such as a handheld interrogation unit, the ICD thus furnishing cardiac resynchronization therapy along with LAP measurement, thereby providing physicians with a powerful system to better manage the treatment of heart failure patients.